Recycling of Plastics

ImpEE

IMPRO

VIN

G

ENG

INEERIN

G

EDU

CA

TION

PROJECT

THE

• 3 million tonnes of waste plastic are produced a year in the UK.

• 1 tonne = 20,000 plastic bottles

• 7% of this is recycled at present (2005)

• An estimated 9.2 billion plastic bottles are disposed of each year

• 200,000 tonnes of plastic rubbish is being sent 8,000 miles to China each year for recycling.

Plastic waste in the UK

Things to think about...•The basic raw materials for plastic

are petroleum and/or natural gas.

•Although plastics only consume around 4% of the world’s oil, supplies are becoming depleted.

•Many plastic products are reaching the end of their lifecycle, forming non-biodegradable mountains of waste plastic.

• 11% of household waste is plastic, 40% of which is plastic bottles

Biologically produced plastics• PHA , PHB and PLA are

biologically produced.

•Processing energy is relatively high.

•More fossil fuel energy is used in their production than for both Polyethylene and PET.

• So renewable plastics are not necessarily as environmentally friendly as they first appear.

0

50

100

150

PHA

PHB

PLA PE PET

Nyl

on

Energy Raw Material

Energy consumption of Biological versus Crude Oil derived plastics

Foss

il Fu

el R

equi

rem

ent

[MJ/

kg o

f pla

stic

]

Assessing embodied energy and CO2

The energy input during manufacturing is not calculated via thermodynamics because:• Industrial processes have varying efficiencies ranging from a few % to

about 50%• The scrap-fraction ranges from a few % to 80% or more• Some part of the energy to heat, light and maintain the plant must be

included• In any new enterprise there is an energy “mortgage” to be paid – the

energy it cost to build the plant

Instead it is calculated by input-output analysis

Production plant

Energy in (MJ/hour) Products out (n/hour)

Energy/product = Energy in/Products out

Assessing embodied energy and CO2 of plastics

Oil derivatives (with embodied energy) PET

production plant

Total plant energy(inc. transport, heat, light…)

Energy mortgage

Bottleblow-

moldingplant

Total plant energy(inc. transport, heat, light…)

Energy mortgage

PET granules (with aggregated embodied energy)

EXAMPLE: primary production of PET bottles

Energy/bottle =

number of bottles out∑ total energy in

Energy/kg PET =

kg of PET out∑ total energy in

Life-Cycle Analysis

• In addition to the energy embodied in the plastic during production and manufacturing, products also require energy during use and disposal.

• An analysis that considers this whole process is referred to as life-cycle analysis.

• The next slide shows the results of such an analysis of a plastic drink container.

Energy breakdown for PE bottle

Glass PE PET Alu Steel

ContainerType

Mass[g]

325 38 25 20 45Mass/volume

[g/litre] 433 38 62 45 102Energy/Mass

[MJ/kg] 14 80 84 200 23Energy/Volume

[MJ/litre] 8.2 3.2 5.4 9.0 2.4

Eco-impact per unit of functionFunction: contain 1 litre of fluid

Recycling changes the picture a little – but not simple

The winner is steel.

The losers are glass and aluminium.

Things to think about • Plastics are not necessarily the waste and

energy culprits that some people think they are. Plastics can be very energy efficient.

• It takes less energy to manufacture a plastic ketchup bottle than a glass ketchup bottle. And since plastics are lightweight, it takes less energy to transport a truckload of plastic ketchup bottles than a truckload of glass ketchup bottles.

• Up to 40% less fuel is used to transport drinks in plastic bottles compared to glass bottles

Why Recycle?• In landfill, both

synthetic and naturally occurring polymers don’t get the necessary exposure to UV and microbes to degrade.

• Here they are taking up space and none of the energy put into making them is being reclaimed.

Photo of tip.

Why Recycle?

• Reclaiming the energy stored in the polymers can be done through incineration, but this can cause environmental damage by release of toxic gases into the atmosphere.

• Recycling is a viable alternative in getting back some of this energy in the case of some polymers.

• As petroleum prices increase it is becoming more financially viable to recycle polymers rather than produce them from raw materials.

Recycling of polymers: the reality

Why, if recycling is energy-efficient? And is it?•Collection is time-intensive, so expensive•Sorting of mixed plastic waste is difficult – contamination

is inevitable.•Removing labels, print, all but impossible at 100% success

rate•Contamination of any sort compromises re-use in “hi-tech”

applications (a carbonated water bottle is a pressure vessel – a failure is unacceptable to the supermarkets that sell them)

In-house scrap (generated at the source of production) is near-100% recycled already.

The consequence: most plastic (apart from in-house) is reused in lower-grade applications•PET: cheap carpets, fleeces•PE and PP: block board, park benches

Recycling of used plastics (here PET bottles): few plastic recycling plants make a profit. Many have closed.

• PET and PVC have many problems with cross contamination as the two polymers appear very similar to the naked eye and share the same specific gravity so cannot be separated by conventional float-sink techniques used in the plastic recycling industry.

• The correct separation of plastics is extremely important. Just one PVC bottle in a batch of 10,000 PET bottles can ruin the entire melt!

Problems with recycling plastics

Energy (and use) audit of recycling of PET

Used plastic bottles (inc. collection transport energy)

Polymersorting,

cleaning, dicing,

packaging plant

Total plant energy(inc. transport, heat, light…)

Energy mortgage

Recycled PET granules (with aggregated embodied energy

-- and contaminates)

Plant for use of recycled PET

Energy mortgage

Total plant energy(inc. transport, heat, light…)

kg of fleece out

Energy per kg of fleece =

kg of fleece out∑total energy in

Energies and prices of virgin and recycled plastics

Commodityplastics

Embodied energy, virgin material

(MJ/kg)

Price*,virgin material

($/kg)

Embodied energy, recycled material

(MJ/kg)

Price*,recycled

material ($/kg)

HDPE 77 - 85 1.9 – 2.0 ≈ 35 - 45 0.84 – 0.97

PP 75 - 83 1.8 – 1.85 ≈ 35 - 45 0.99 – 1.1

PET 79 - 88 2.0 – 2.1 ≈ 60 - 64 1.1 – 1.2

PS 96 - 105 1.5 – 1.6 ≈ 40 - 50 0.75 – 0.86

PVC 63 - 70 1.4 – 1.5 ≈ 35 - 40 0.77 – 0.99

*Spot prices, November 2005

The messages:•Both the embodied energy and price of recycled plastics are about half that of

virgin material•The lower price reflects the lower quality of the recycled material, limiting its use•Because of this the contribution of recycling to current plastic consumption is

small

Recycling of polymers: the reality

0

1

2

3

4

5

HDPE PP PET PS PVC

Virgin Production Recycled Production

Because of the problems outlined on the previous slides, the contribution of recycling to current plastic consumption is small.

Plas

tic p

rodu

ctio

n (

mill

ions

of t

onne

s /

year

)

Things to think about?

• Since most oil is extracted to be burned directly as fuel, is it so wrong to turn it into plastic first, and then burn it to recover the energy?

Things to think about

• China drives the global waste trade, importing more than 3 million tonnes of waste plastic a year.

• Western plastic companies are setting up in China, but some of the poorest people are employed to sort and recycle the plastic.

• Is it better to send rubbish to China to be recycled than to put it in landfill in Britain?

How plastics are sorted

How the recycling occurs1. The recyclables can be collected from individual

homes or from collection points such as tips, schools and supermarkets. After transport to the recycling plant, plastics are hand sorted according to their recycling code. Some materials recovery facilities can mechanically sort different plastic codes. Each plastic type is processed separately.

How the recycling occurs2.The plastic is sliced into flakes and the flakes go

through a washing process.

3.The clean plastic flakes are melted together, extruded through small holes, and chopped into pellets.

How the recycling occurs4.The bags of recycled plastic pellets are taken to

factories where they are melted and made into new products.

5.In the case of soft drink bottles the recycled pellets are combined with virgin material fresh from petroleum. These are then melted and moulded into preforms.

How the recycling occurs6.The bottles are blown into another mould to

form the full size bottle this is often done at the bottling plant where they are filled and sealed.

7.Once consumed they are delivered back to the recycling plant after household recycling.

Recycling Statistics

4%3%

5%

16%15%

Fiber57%

FiberStrappingFood/Beverage ContainersNon-Food containersFilm SheetOther

Where Recycled PET Ends Up

Other includes: Compounded Resin (2%), Tolled (1%), Clean Export (1%)

A different viewpoint...

• It takes one day to collect a kilo of thin plastic bags from a tip by hand

• For one kilo, the rag picker typically earns R1.5 in India

• Some cities in India are banning the use of thin plastic bags

ImpEE is based at the Department of Engineering at the University of Cambridge and is funded by the CMI Institute.

© University of Cambridge, 2005

This material was produced as a part of the ImpEE Project at the University of Cambridge. It may be reproduced, modified and used freely for

educational purposes.